Abstract

Polyvinylidene fluoride hydrophones are being used to an increasing extent to study the acoustic pressure waveform and frequency content of broadband ultrasonic pulses. Simple optical techniques have recently been developed which also have the potential for obtaining this information. In this study broadband ultrasonic pulses transmitted by five common medical ultrasound transducers into distilled water were sampled in the transducerfocal plane with a commerical piezoelectrical polymer hydrophone (Nuclear Associates model 84‐403) and a broadband optical diffraction technique [W. A. Riley, L. A. Love, and D. W. Griffith, J. Acoust. Soc. Am. Suppl. 1 69, S91 (1981)]. Although the hydrophone is an approximate point (0.5‐ram‐diam) detector and the optical technique a line detector, the temporal waveforms obtained which correspond to the time variation of the acoustic pressure in the focal plane were very similar. The fast Fourier transforms of the digitally sampled waveforms were also obtained and compared. The fiat frequency response of the optical technique over the frequency range from 2.0–10 MHz was used to calibrate the frequency response of the hydrophone which was found to vary by as much as ±3 dB over this range. The results clearly demonstrate that under the experimental conditions studied, consistent estimates of the acoustic pressure waveform can be obtained with either a hydrophone probe or the optical line probe. Since the hydrophone is delicate, easily damaged and susceptible to prolonged immersion in water, the optical technique may be preferable in some applications. [Work supported by NIGMS 27755.]